1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing a high purity polycrystalline silicon.
2. Description of the Related Art
A polycrystalline silicon is used as a raw material of a monocrystalline silicon for a semiconductor or a raw material of a silicon for a solar cell. In recent years, according to the situation in which a diffusion of a solar cell is greatly expanded, a demand of a polycrystalline silicon have been increasing as a raw material of the solar cell in particular.
However, as a polycrystalline silicon that is a raw material of a silicon for a solar cell, it is a present situation that a scrap such as a crucible residue after a monocrystalline silicon for a semiconductor is removed and a cutting abatement debris of a monocrystalline silicon ingot is used. Consequently, since a polycrystalline silicon to be used for a solar cell depends on a trend of the semiconductor industry in quality and quantity, the polycrystalline silicon is in short supply chronically as the situation now stands.
The Siemens method can be mentioned as a typical method for manufacturing a high purity polycrystalline silicon that is a raw material of a monocrystalline silicon for a semiconductor. For the Siemens method, a high purity polycrystalline silicon can be obtained by the hydrogen reduction of trichlorosilane (HSiCl3) (see Japanese Patent No. 2867306 (Japanese Patent Application Laid-Open Publication No. 5-139891)).
For the common Siemens method, as shown by a manufacturing apparatus 10 in FIG. 5, a silicon seed rod 50 is disposed in a water-cooled reaction vessel 30 of a bell jar type, an electricity is conducted in the silicon seed rod 50 to heat the seed rod 50 up to approximately 1000° C., trichlorosilane (HSiCl2) and hydrogen (H2) as a reducing agent are introduced into the reaction vessel 30 from the bottom side to reduce silicon chloride, and a generated silicon adheres to the surface of the seed rod 50 selectively, thereby obtaining a rod shaped polycrystalline silicon. The Siemens method has the advantage related to an apparatus that an atmosphere can be easily sealed since the reaction vessel 30 itself is cooled in addition to the advantage that a raw material gas can be vaporized at a comparatively low temperature. Consequently, the Siemens method has been in widespread use and adopted extensively.
However, since the seed rod 50 is heated by a current conduction for the Siemens method, an excessive current must be flown to heat the seed rod as the rod shaped silicon is grown by an adhesion of a polycrystalline silicon and an electrical resistance is decreased by a gradual process. Consequently, a growth limit exists due to a balance with an energy cost, and the running of a manufacturing facility is in a batch system, thereby deteriorating a production efficiency. Moreover, an electric power consumption rate is large to a cost of a polycrystalline silicon in a product unfortunately.
As a method for manufacturing a polycrystalline silicon other than the Siemens method, a method by a reduction of silicon tetrachloride (SiCl4) using a metal reducing agent can be mentioned for instance (see Japanese Patent Application Laid-Open Publication No. 2003-34519 and Japanese Patent Application Laid-Open Publication No. 2003-342016). To be more precise, a silicon tetrachloride gas and a zinc (Zn) gas are supplied into a horizontal reaction vessel made of quartz heated to approximately 1000° C., thereby growing a polycrystalline silicon in the reaction vessel.
For the above method, zinc chloride (ZnCl2) obtained as a by-product material can be separated into zinc and chlorine by a method such as electrolysis, the obtained zinc can be used as a reducing agent again, and the obtained chlorine can be reacted to an inexpensive metal silicon to synthesize a silicon tetrachloride to be used as a raw material gas. In that case, a recycling-oriented process can be constructed. Consequently, there is a possibility that a polycrystalline silicon can be manufactured at a low cost.
It is general that a solid is fused to be liquid in a vessel and gasified in the same vessel in order to change a metal from a solid to a gas (see Japanese Patent Application Laid-Open Publication No. 60-161327).
In the case in which zinc is gasified by such a method, a production efficiency of a zinc gas is deteriorated. Moreover, in the case in which a zinc granule is put into a vessel heated to be a boiling point or higher of zinc, there is a possibility that powdered zinc or granulated zinc is partially burnt in the vessel. Furthermore, it is difficult to increase or decrease an input amount of additional zinc. In the case in which the input amount is too large, a fusing temperature in the vessel is greatly reduced, and a stable amount of evaporation of a zinc gas cannot be obtained unfortunately.
Moreover, for an apparatus for manufacturing a high purity polycrystalline silicon, in which such a fusing evaporator of zinc has been adopted, a polycrystalline silicon to be obtained by a reaction is easily affected by a pollution from a reactor material since the polycrystalline silicon is grown from a reactor wall, thereby deteriorating a production efficiency of a polycrystalline silicon unfortunately.    Patent document 1: Japanese Patent No. 2867306 (Japanese Patent Application Laid-Open Publication No. 5-139891)    Patent document 2: Japanese Patent Application Laid-Open Publication No. 2003-34519    Patent document 3: Japanese Patent Application Laid-Open Publication No. 2003-342016    Patent document 4: Japanese Patent Application Laid-Open Publication No. 60-161327